The different levels are related to different human modalities.
We say that level 1 is grounded into socioperception, an ability that humans developed for collaboration that is crucial for achieving joint attention [1]}. Level 2 is grounded in hearing if we use speech as our communication channel. Level 3 is grounded in vision when it involves recognizing referents in the real world.
Level 4 is grounded in kinesthetic when it involves moving and acting in the real world. The classification, along with obstacles that the addressee may face in the various modalities during the interpretation of a conversational action, is shown in Table REF . In the rest of the paper we will refer to these modalities using the level number.
<TABLE>